Regulating the temperature of a battery in a low-speed, high-altitude, long-endurance aircraft is difficult. Protecting the battery from the cold without significant heating power requires very good insulation, but the insulation makes it necessary to cool the battery when it gets hot during periods of heavy use. Common solutions for controlled cooling all involve moving parts, which are of particular concern on long endurance flights, so that a solution that minimizes additional heating burden while providing high reliability is thus desired.
For terrestrial applications, cooling fans are the near-universal standard for system temperature control. This works fine, but has potential reliability issues for a long endurance aircraft. More importantly, however, is that high altitude air is too thin for effective use of cooling fans. Venting air from an aircraft's incoming airstream, while another option, poses a question of how to ensure the system will not fail in a potentially detrimental way.